1. Field of the Invention
The present invention relates to a plasma treating method and apparatus therefor, and more particularly to a plasma treating method and apparatus therefor which is suitable for etching and film-forming treatment such as a specimen of a substrate of a semiconductor utilizing a gas plasma while controlling a temperature thereof to a low level not higher than 0.degree. C.
2. Description of the Prior Art
In prior art for effecting etching and film-forming treatment utilizing a gas plasma while controlling a temperature of a substrate of a semiconductor element or the like to a low temperature not higher than 0.degree. C., a liquid refrigerant, for example, liquid nitrogen, a liquified fluorine compond, liquid helium, etc. having a temperature not higher than 0.degree. C. is supplied into a specimen table on which a specimen is placed to cool the specimen table, and a temperature of the specimen is controlled to a predetermined low temperature not higher than 0.degree. C.
Documents relevant to the art of the kind as described above are, for example, unexamined published Japanese Patent Application No. 240635/1986, unexamined publication Japanese Utility Model Application No. 103249/1987 and so forth.
For example, in the case where the apparatus stops or is out of operation when the apparatus is maintained and checked, the liquid refrigerant retained within the specimen table is discharged outside the table. However, in the aforementioned prior art, recovery of the liquid refrigerant from the specimen table is not at all taken into consideration. That is, the liquid refrigerant is wastefully discarded outside the specimen table and therefore, the quantity of liquid refrigerant consumed increases to increase the operation cost of the apparatus. In addition, for example, the treating chamber interiorly provided with the specimen table is sometimes opened to the atmosphere for maintenance and check of the apparatus. However, in such a case, when the specimen table cooled to a low temperature not higher than 0.degree. C. is exposed to the atmosphere in that state, moisture or the like in the atmosphere is adsorbed by the specimen table. This gives rise to problems in that time required for pressure reduction and exhaust within the treating chamber after maintenance and check of the apparatus is extended and that the interior of the treating chamber cannot be reduced to a predetermined pressure as the case may be. This problem similarly occurs, for example, in the case where nitrogen gas or the like is sealed into the treating chamber until the next day's operation starts, the specimen table cooled to a low temperature not higher than 0.degree. C. is maintained in that state and the operation of the apparatus is stopped.